X-ray tube control means



Aug. 1, 193.9.

Filed Sept. 30, 1938 INVENTOR EDWIN R. GOLDFIELD ATTORNEYJ Patented Aug. 1, 1939 UNITED STATES TENT OFFIQE X-RAY TUBE CONTROL MEANS corporation of Ohio Application September 30, 1938, Serial No. 232,61?

3 Claims.

This invention relates to X-ray tube control means and more particularly to means for easily and accurately presetting the filament temperature of an X-ray tube in order to be able to obtain a desired milliamperage through the tube.

Current is ordinarily supplied to the filament of an X-ray tube through a filament transformer. The usual method of determining the current flowing in the filament has been to connect a voltmeter across the two leads of the filament transformer primary and to adjust the current in the transformer primary 'to produce a certain reading on this voltmeter. A chart was then necessary to indicate the reading of the voltmeter for any desired milliamperage in the tube filament. The difiiculty with this arrangement was not only the disadvantage of having to consult a chart for each setting but also the necessity; of reading the voltmeter extremely accurately because a very small change in the voltage through the filament of the X-ray tube produces a comparatively large change in the milliamperage through the tube.

- An object of the present invention is to provide means very easily operated and adapted to very accurately set the tube control to provide a predetermined current flow through the tube filament. The means by which this is done will be more fully set forth in the specification and drawing and the essential features will be defined in the claims.

In the drawing, Fig. l is a diagram showing one embodiment of my invention. This diagram shows an X-ray tube at 2 having a filament 2a. Operating current for the tube is supplied from the secondary 3a of the transformer 3 Whose primary 3b is connected to a current source L1, L2 through an autotransformer l. A meter 5 is provided for reading the milliamperes flowing in the transformer secondary 3a, the connection here shown being a half-wave rectification. It will be understood that my invention is applicable to any X-ray tube no matter what its degree of rectification or by what means the rectification is supplied. Current for the filament 2a is supplied from the secondary 6a of the filament transformer 6 whose primary 6b is connected by conductors l and 8 with suitable points on the autotransformer 4. Means indicated at 9 is provided for varying the current supplied to the filament transformer primary 6b. This means may take the form of a variable inductance or a variable resistance.

The means provided for accurately presetting the filament current comprises one or more variable resistances as shown at Illa, ltb, Hlc and Id, adapted to be connected in series with a voltmeter or milliammeter H by means of a switch l2. The variable resistance is connected by conductor is to the conductor 1 and the milliammeter is connected by conductor It to conductor 8. Preferably but not necessarily a rheostat I5 is supplied in series with the voltmeter circuit which is adapted to be preset depending upon the kilovoltage impressed upon. the X-ray tube 2. For the purposes of this invention the meter H may be of the type shown in Fig. 2 having a needle Ma and a predetermined indication llb.

In setting up the above named measuring circuit the switch I2 is placed on the contact Illa so as to place the variable resistance lEla in series with the milliammeter H and the resistance Illa is then set at a more or less permanent setting so that a predetermined milliamperage flows through the filament 2a when the adjusting means 9 is moved to position the needle Ila on the indication lib. This milliamperage may be indicated on the dial of the switch l2. Where a plurality of filament currents are desired a plurality of variable resistances are supplied, arranged to be selectively connected between the switch [2 and the conductor It as shown in the drawing. Each of the resistances 56b, H10 and llld is preset as described for resistance Illa, so that when the switch l2 engages their respective contacts and the adjusting means 9 is set until the needle i la registers with the indication Ilb, various predetermined milliamperage will flow through the filament 2a as indicated on the dial of the switch l2. As many such settings of switch l2 may be provided as desired.

The rheostat l5 may be supplied if desired when various kilovoltages are to be applied to the tube 2. The dial of the rheostat is then graduated in peak kilovolts and this adjustment is coordinated with the setting of the resistances l and the indication on the voltmeter I I so that when the rheostat I is set for the kilovolts impressed on tube 2 and the switch I2 is placed on one of the contacts such as Illa, then when the adjusting means 9 is moved to cause the needle Ha to register with the indication ill) the milliamperage flowing through the filament 2a will be that indicated on the dial of the switch l2. It is well known to those skilled in this art that with the filament temperature held constant the variation in kilovoltage impressed upon the X-ray tube causes a slight change in the milliamperage flowing through the tube fi1ament. The rheostat takes care of this.

The device is generally satisfactory without the rheostat I5 because the efiect on filament current of variations in the kilovolts impressed on the X-ray tube is not great enough to cause unsatisfactory results within the limits of practical or usual operation.

The operation of my improved control is thus very simple. Once the device has been assembled and adjusted it is only necessary to first set rheostat I 5 to the kilovoltage impressed on the X-ray tube, then move the switch I2 to the desired filament milliamperage indicated on the dial of switch l2 and then turn the adjusting means 9 until the needle Ila registers with the indication MD on the voltmeter II. Any one can do this and obtain a very accurate setting.

My invention conserves the life of the X-ray tube because it takes at least one second to make an accurate reading at meter 5 of the milliamperes flowing in the tube circuit. There is thus a great waste of time in setting the adjusting means 9 and reading meter 5 to get an accurate setting for a radiograph requiring, say, one one-hundredth of a second. With the device here disclosed the rough setting is already accomplished at resistance l0 and the final adjustment at 9 is easy because the needle Ila is always brought to the single mark I lb.

In the claims wherever milliammeter or milliamperes occurs, it will be understood that voltmeter and volts respectively are equivalents.

What I claim is:

1. An X-ray apparatus comprising an X-ray tube, a source of high-tension current therefor and a filament transformer having its secondary connected with the tube filament and having it's primary connected by a pair .of conductors with a source of current, the combination of means for varying the current in said transformer primary, a selector switch having a plurality of contacts, a plurality of variable resistances, one for each of said contacts, said resistances being connected between said contacts and one of said conductors, a milliammeter connected in series between said switch and the other of said conductors, said milliammeter having a predetermined indication,

and said indication and each of said resistances being so arranged that placing one of said resistances in series with said milliammeter by means of said switch and varying the current in said transformer primary until said milliammeter registers with said indication will cause a predetermined current flow in said tube filament.

2. In X-ray apparatus comprising an X-ray tube, a source .of high-tension current therefor and a filament transformer having its secondary connected with the tube filament and having its primary connected by a pair of conductors with a source of current, the combination of means for varying the current in said transformer primary, a selector switch having a plurality of contacts, a plurality of variable resistances, one for each of said contacts, said resistances being connected between said contacts and one of said conductors, a milliammeter connected in series between said switch and the other of said conductors, a rheostat in series with said milliammeter and graduated in kilovolts, said milliammeter having a pre determined indication, and said indication and said rheostat and each of said resistances being so arranged that setting of said rheostat for the kilovolts impressed on said X-ray tube and placing one of said resistances in series with said milliammeter by means of said switch and varying the current in said transformer primary until said milliammeter registers with said indication will cause a predetermined current flow in said tube filament. H

3. In an X-ray apparatus, means for supplying current to the filament of an X-ray tube including two conductors, means for varying said current supply means, means for indicating the current supplied and electrically connected between said conductors including a variable resistance and a milliammeter in series, said resistance being preset to indicate a predetermined current supply to said filament only when said second named means is adjusted to cause said milliammeter to move to a predetermined indication, and an adjustable rheostat in series with said milliammeter, said rheostat having predetermined settings to vary said milliammeter reading to compensate for variations in filament current due to voltage impressed on the tube.

EDWIN R. GOLDFIELD. 

